Data-modulated pilots for phase and gain detectors

ABSTRACT

Methods, systems, and devices are described for mitigating an unwanted increase in a coding rate of a wireless communication signal. A plurality of symbols including a transmitted codeword is received. The plurality of symbols including a first group of data symbols with a first modulation and coding scheme and a second group of data modulated pilot symbols with a second modulation and coding scheme. Applicable demodulation schemes are adaptively switched for each group of the plurality of symbols. The second group of data modulated pilot symbols are used in lieu of pilot symbols. The second modulation and coding scheme is a more reliable modulation and coding scheme than the first modulation and coding scheme.

CROSS REFERENCES

The present Application for Patent claims priority to U.S. ProvisionalPatent Application No. 61/745,484 by Gotman et al., entitled“Data-Modulated Pilots for Phase and Gain Detectors,” filed Dec. 21,2012, assigned to the assignee hereof, and expressly incorporated byreference herein.

BACKGROUND

The following relates generally to wireless communication, and morespecifically to phase detection and coding gains. Wirelesscommunications systems are widely deployed to provide various types ofcommunication content such as voice, video, packet data, messaging,broadcast, and so on. These systems may be multiple-access systemscapable of supporting communication with multiple users by sharing theavailable system resources (e.g., time, frequency, and power). Examplesof such multiple-access systems include code-division multiple access(CDMA) systems, time-division multiple access (TDMA) systems,frequency-division multiple access (FDMA) systems, and orthogonalfrequency-division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communications system may includea number of base stations, each simultaneously supporting communicationfor multiple mobile devices. Base stations may communicate with mobiledevices on downstream and upstream links. Each base station has acoverage range, which may be referred to as the coverage area of thecell. A transmitter (e.g., a base station) and a receiver (e.g., amobile device) may include, respectively, components for signaltransmissions and signal reception. For example, the transmitter andreceiver may each include one or more oscillators. These oscillators maynot be in sync with one another, and may have inherent imperfections. Asa result, phase noise may be introduced into the received signal. Thisnoise may create difficulties for the receiver to correctly determinethe phase for symbols transmitted to the receiver. Currently, phaseerror is determined by performing hard decisions on the received symbolsthemselves. However, due to the noisy conditions at the receiver, thishard decision may regularly be incorrect. To improve hard decisions,known pilot sequences are inserted into a stream of data symbols. Theuse of pilot sequences however, reduces the number of symbols that areavailable to carry data. Thus, the coding rate of the data stream isincreased in order to maintain a desired level of data throughput.

SUMMARY

Methods, systems, and devices are described for mitigating an unwantedincrease in a coding rate of a wireless communication signal. Aplurality of symbols including a transmitted codeword is received. Theplurality of symbols including a first group of data symbols with afirst modulation and coding scheme and a second group of data modulatedpilot symbols with a second modulation and coding scheme. The secondgroup of data modulated pilot symbols are used in lieu of pilot symbols.By replacing pilot symbols with symbols that carry data, an undesirableincrease in the coding rate of the plurality of symbols is mitigated atthe transmitter and the desired data throughput is not sacrificed.

At the receiver, applicable demodulation schemes are adaptively switchedfor each group of the plurality of symbols. The second modulation andcoding scheme is a more reliable modulation and coding scheme than thefirst modulation and coding scheme. In addition, a priori LLRs may begenerated for each symbol of the received plurality of symbols, whereasLLRs may not be generated for pilot symbols in a data stream. Theadditional LLRs may improve the performance of a decoder to decode thetransmitted codeword.

A method to mitigate an unwanted increase in a coding rate of a wirelesscommunication signal is described. A plurality of symbols including atransmitted codeword may be received. The plurality of symbols mayinclude a first group of data symbols with a first modulation and codingscheme and a second group of data modulated pilot symbols with a secondmodulation and coding scheme. An adaptive switching between applicabledemodulation schemes for each group of the plurality of symbols mayoccur.

In one configuration, the second group of data modulated pilot symbolsmay be used in lieu of pilot symbols. A carrier phase error may bedetermined based at least in part on the second group of data modulatedpilot symbols. The second modulation and coding scheme may be a morereliable modulation and coding scheme than the first modulation andcoding scheme.

Adaptively switching between the demodulation schemes may includedetermining, for each symbol, whether the symbol occurs when a pilotsymbol is expected to occur. Upon determining that the symbol does notoccur when a pilot symbol is expected to occur, a first look-up table ora first non-LUT function for the first modulation and coding scheme maybe used to perform hard decision decoding of the symbol. Upondetermining that the symbol does occur when a pilot symbol is expectedto occur, a second look-up table or a second non-LUT function for thesecond modulation scheme may be used to perform hard decision decodingof the symbol.

In one example, phase errors for each symbol of the plurality ofreceived symbols may be generated using the results of the hard decisiondecoding. Phase corrections for each symbol of the plurality of receivedsymbols may be generated based on the generated phase errors.

The symbols of the plurality of received symbols may be derotatedaccording to generated phase corrections for the symbols. A plurality ofa priori log-likelihood ratios (LLRs) may be generated from theplurality of phase corrected received symbols. The plurality of LLRs mayrepresent a plurality of bits of the transmitted codeword. Generatingthe plurality of a priori LLRs may include determining, for each phasecorrected symbol, whether the phase corrected symbol occurs when a pilotsymbol is expected to occur. Upon determining that the phase correctedsymbol does not occur when a pilot symbol is expected to occur, a firstnumber of a priori LLRs may be generated from the phase correctedsymbol. Upon determining that the phase corrected symbol does occur whena pilot symbol is expected to occur, a second number of a priori LLRsmay be generated from the phase corrected symbol. The second number ofLLRs may be less than the first number of LLRs.

In one embodiment, the plurality of a priori LLRs may be fed to adecoder to decode the transmitted codeword. A plurality of soft aposteriori LLRs may be collected at the output of the decoder. The softLLRs may represent the plurality of bits of the transmitted codeword.

In one configuration, the plurality of received symbols may be adigitized representation of at least a portion of a wirelesscommunication signal. The first modulation scheme may be 1024 QuadratureAmplitude Modulation (QAM). The second modulation scheme may be 64 QAM.

A receiving device configured to mitigate an unwanted increase in acoding rate of a wireless communication signal is also described. Thedevice may include a processor and memory in electronic communicationwith the processor. Instructions may be stored in the memory. Theinstructions may be executable by the processor to receive a pluralityof symbols including a transmitted codeword. The plurality of symbolsmay include a first group of data symbols with a first modulation andcoding scheme and a second group of data modulated pilot symbols with asecond modulation and coding scheme. The second group of data modulatedpilot symbols may be used in lieu of pilot symbols. The instructions mayalso be executable by the processor to adaptively switch betweenapplicable demodulation schemes for each group of the plurality ofsymbols.

An apparatus to mitigate an unwanted increase in a coding rate of awireless communication signal is also described. The apparatus mayinclude means for receiving a plurality of symbols including atransmitted codeword. The plurality of symbols may include a first groupof data symbols with a first modulation and coding scheme and a secondgroup of data modulated pilot symbols with a second modulation andcoding scheme. The second group of data modulated pilot symbols may beused in lieu of pilot symbols. The apparatus may further include meansfor adaptively switching between applicable demodulation schemes foreach group of the plurality of symbols.

A computer program product for mitigating an unwanted increase in acoding rate of a wireless communication signal is also described. Thecomputer program product may include a non-transitory computer-readablemedium storing instructions executable by a processor to receive aplurality of symbols including a transmitted codeword. The plurality ofsymbols may include a first group of data symbols with a firstmodulation and coding scheme and a second group of data modulated pilotsymbols with a second modulation and coding scheme. The second group ofdata modulated pilot symbols may be used in lieu of pilot symbols. Theinstructions may be executable by the processor to adaptively switchbetween applicable demodulation schemes for each group of the pluralityof symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 shows a block diagram of a wireless communications system;

FIG. 2 shows a block diagram of a transmitter device illustratingvarious embodiments of the invention;

FIG. 3 shows a block diagram of a receiver device illustrating variousembodiments of the present systems and methods;

FIG. 4 is a block diagram illustrating one embodiment of a receivermodule in accordance with the present systems and methods;

FIG. 5 is a block diagram illustrating one embodiment of a receivermodule in accordance with the present systems and methods;

FIG. 6 is a block diagram illustrating one example of a receiver modulethat may implement the present systems and methods;

FIG. 7 is a block diagram of a system including a base station and amobile device;

FIG. 8 is a flow chart illustrating one example of a method to mitigatean undesirable increase in a coding rate of a wireless communicationsignal in accordance with the present systems and methods;

FIG. 9 is a flow chart illustrating one example of a method to improveaccuracy of hard decisions of symbols of a wireless communication signalin accordance with the present systems and methods; and

FIG. 10 is a flow chart illustrating one example of a method to improvethe decoding of a codeword in accordance with the present systems andmethods.

DETAILED DESCRIPTION

Methods, systems, and devices are described for mitigating an unwantedincrease in a coding rate of a wireless communication signal. In oneexample, a plurality of symbols comprising a transmitted codeword isreceived. The plurality of symbols may include a first group of datasymbols with a first modulation and coding scheme and a second group ofdata modulated pilot symbols with a second modulation and coding scheme.As the first group and second group of symbols are demodulated in areceiver, different demodulation schemes are adaptively used for eachgroup of the plurality of symbols. In one example, the second group ofdata modulated pilot symbols are used in lieu of pilot symbols (e.g.,reference signals) in a data stream. The second modulation and codingscheme may be a more reliable modulation and coding scheme than thefirst modulation and coding scheme. By using available symbols to carrydata, instead of replacing these data symbols with pilot symbols, thecoding rate applied to a data stream may be reduced without sacrificingdata throughput.

Referring first to FIG. 1, a block diagram illustrates an example of awireless communications system 100. The system 100 includes basestations 105 (or cells), communication devices 115, a base stationcontroller 120, and a core network 130 (the base station controller 120may be integrated into the core network 130). The system 100 may supportoperation on multiple carriers (waveform signals of differentfrequencies). Multi-carrier transmitters can transmit modulated signalssimultaneously on the multiple carriers. For example, each modulatedsignal may be a multi-carrier channel modulated according to the variousradio technologies described above. Each modulated signal may be sent ona different carrier and may carry control information (e.g., pilotsignals, control channels, etc.), overhead information, data, etc. Thesystem 100 may be a multi-carrier LTE network capable of efficientlyallocating network resources. In some cases, the system 100 may supportoperation using a single carrier. The system 100 may be a networkcapable of operating using time division multiplexing (TDM), timedivision multiple access (TDMA), frequency division multiple access(FDMA), single-carrier FDMA (SC-FDMA), code division multiple access(CDMA), or orthogonal frequency division multiple access (OFDMA).

The base stations 105 may wirelessly communicate with the devices 115via a base station antenna (not shown). The base stations 105 maycommunicate with the devices 115 under the control of the base stationcontroller 120 via multiple carriers. Each of the base station 105 sitesmay provide communication coverage for a respective geographic area. Insome embodiments, base stations 105 may be referred to as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a basic service set (BSS), an extended service set (ESS), aNodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or some other suitableterminology. The coverage area for each base station 105 here isidentified as 110-a, 110-b, or 110-c. The coverage area for a basestation may be divided into sectors making up only a portion of thecoverage area (e.g., sectors 112-b-1, 112-b-2, 112-b-3, etc.). Thesystem 100 may include base stations 105 of different types (e.g.,macro, micro, and/or pico base stations). There may be overlappingcoverage areas for different technologies. A macro base station mayprovide communication coverage for a relatively large geographic area(e.g., 35 km in radius). A pico base station may provide coverage for arelatively small geographic area (e.g., 12 km in radius), and a femtobase station may provide communication coverage for a relatively smallergeographic area (e.g., 50 m in radius). There may be overlappingcoverage areas for different technologies.

The devices 115 may be dispersed throughout the coverage areas 110. Eachdevice 115 may be stationary or mobile. In one configuration, thedevices 115 may be able to communicate with different types of basestations such as, but not limited to, macro base stations, pico basestations, and femto base stations, via link 125. The devices 115 may bereferred to as mobile stations, mobile devices, access terminals (ATs),user equipments (UEs), subscriber stations (SSs), or subscriber units.The devices 115 may include cellular phones and wireless communicationsdevices, but may also include personal digital assistants (PDAs), otherhandheld devices, netbooks, notebook computers, tablet computers, etc.

In one example, the base station controller 120 may be coupled to a setof base stations and provide coordination and control for these basestations 105. The base station controller 120 may communicate with thebase stations 105 via a backhaul (e.g., core network 130). The basestations 105 may also communicate with one another directly orindirectly and/or via wireless or wireline backhaul.

Various components of the devices 115 may add interference (i.e., noise)to a received signal. For example, phase noise may be introduced byfrequency oscillators within the devices 115. A digital phase-lockedloop (DPLL) may be used in the modem's receive path of the devices 115for carrier wave recovery. The DPLL may track the carrier frequency andphase and estimate phase corrections to apply on a plurality of receivedsymbols. The DPLL may be fed with phase errors produced by a phasedetector (PD). The phase errors may be produced by comparing the actualphases of a plurality of received symbols with the expected phases of aplurality of ideal reference symbols. In some cases, the phase errorsare calculated independently for each symbol. The phase errors may becalculated as a group for a plurality of symbols. In a data aidedimplementation, where there is no a priori knowledge of the transmittedsymbols, the best estimation of the reference symbols is a hard decisiontaken on the current soft symbols (as a closest constellation point).

Since this part of the modem is susceptive to noisy conditions (boththermal and phase noise), the PD may produce a relatively high rate oferroneous hard decisions yielding degradation in the performance of thePD, which may lead to a decrease in the performance of the DPLL. Thismay result in the degradation of the overall performance of the modem ofa device 115. In one example, a sequence of erroneous hard decisions maycause the DPLL to lose track of the carrier's phase or frequency. In oneembodiment, pilot symbols may be inserted into the signal to reduce thelikelihood of producing incorrect hard decisions. In one configuration,the PD may have a priori knowledge of the transmitted symbolrepresenting a received pilot symbol. As a result, when a pilot symboloccurs in the signal, the PD may compare the received symbol (i.e., thepilot symbol) with a correct presumption of the correspondingtransmitted symbol when calculating the phase error. Thus, the denserthe pilot pattern is in a signal, the likelihood of the DPLL losingtrack of the carrier's phase or frequency may be reduced. However, usinga denser pattern of pilot symbols may reduce the data throughput sincepilot symbols may occupy allocations of data symbols of the signal. As aresult, in order to maintain a consistent data throughput, the codingrate of the signal may be increased. In one embodiment, the presentsystems and methods may use data modulated pilot symbols in lieu ofpilot symbols. These symbols may reduce the likelihood of hard decisionerrors produced by the DPLL while maintaining a certain level of datathroughput.

FIG. 2 is a block diagram 200 of a device 105-a which illustratesvarious embodiments. The device 105-a may be an example of a basestation 105 of FIG. 1. In one configuration, the system at issue may useQuadrature Phase Shift Keying (QPSK). However, the present systems andmethods may be implemented using a range of other modulation schemes.

The base station 105-a may include a number of transmitter components,which may include an information source processing module 205, anencoder 210, and a modulator 215. These components of the base station105-a may, individually or collectively, be implemented with one or moreApplication Specific Integrated Circuits (ASICs) adapted to perform someor all of the applicable functions in hardware. Alternatively, thefunctions may be performed by one or more other processing units (orcores), on one or more integrated circuits. In other embodiments, othertypes of integrated circuits may be used (e.g., Structured/PlatformASICs, Field Programmable Gate Arrays (FPGAs), and other Semi-CustomICs), which may be programmed in any manner known in the art. Thefunctions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors. The base station105-a may include one or more memory units used for a variety ofpurposes.

In one configuration, the information source processing module 205 mayprocess an information source. The output of the information sourceprocessing module 205 may be referred to as an information sequence. Theencoder 210 may transform the information sequence outputted from theinformation source into an encoded sequence. The encoded sequence may bereferred to as a codeword. The transformation process performed by theencoder 210 may occur after the information source is encoded, but priorto modulation.

Redundant information may be added by the encoder 210 to protect theinformation sequence against errors which may occur during transmissionof the codeword. The redundant bit stream may be calculated from theinformation sequence. As a result, a correlation may exist between theoriginal information sequence and the redundancy bit stream. Thiscorrelation may be used by a decoder to detect and correct errors thatmay be generated in the channel environment.

In one example, the modulator 215 may combine the encoded sequence fromthe encoder 210 with a carrier signal to render a plurality of symbolsthat include the codeword that are suitable for transmission. Typically,pilots are inserted into the stream of symbols. For example, the encoder210 may be aware of a pattern of pilot symbols and may set a coding rateof the codeword to correlate to the number of symbols allocated to carrydata. The coded bits representing the codeword may be modulated by themodulator 215 to produce data symbols, which may be interleaved withpilot symbols to occupy the available symbols. In another example, theencoder 210 may use a maximum number of symbols, regardless of symbolallocations. Data symbols may be punctured and replaced with pilotsymbols of a known sequence.

The effect of inserting pilots as described above may result in anincrease in the coding rate of the codeword, because less symbols areavailable to carry data regarding the codeword. In the first approach,the encoder 210 may set the coding rate according to the number ofsymbols available for data. In the second approach, data symbols arepunctured and replaced with pilots, effectively increasing the codingrate.

In one embodiment, present systems and methods may minimize the increasein coding rates due to insertion of pilots by using pilot symbols thatcarry data (i.e., data modulated pilot symbols). Data modulated pilotsymbols may be symbols that contain data in a location where a pilotsymbol is expected to occur. In one example, different modulation andcoding schemes (MCS) may be used for different symbols. In one example,pilot symbols may be replaced with data symbols modulated at a second,more reliable MCS. The second, more robust MCS may be selected byidentifying the coded bit error rate (BER) sensitivity signal-to-noiseratio (SNR) level of the first (MCS) and choosing the second MCS forpilot modulation such that the uncoded symbol error rate (SER) may beless than 1% at the identified SNR level. In one example, the datamodulated pilot symbols are modulated using a robust modulation scheme,such as Quadrature Phase Shift Keying (QSPK), while the data symbols aremodulated using a modulation scheme with higher throughput, such as64-bit Quadrature Amplitude Modulation (QAM). While QPSK and 64-bit QAMare used in this example, it is to be understood that other modulationand/or coding schemes may be used in accordance with the various systemsand methods described here.

In some cases, the modulator 215 may combine the encoded sequence fromthe encoder 210 with a carrier signal to render symbols that include thecodeword and are suitable for transmission according to the relevantstandards and/or design parameters in place. Coded bits representing thecodeword may be modulated by the modulator 215 to produce data symbolsand/or data modulated pilot symbols. The modulation may occur using twoor more different modulation and coding schemes. For example, themodulator 215 may encode and modulate data assigned to normal datasymbols using a first modulation and coding scheme while encoding andmodulating the data assigned to data modulated pilot symbols accordingto a second, more robust modulation and coding scheme. The encoder 210and/or modulator 215 may be aware of a pattern of pilot symbols (e.g.,as defined by a standard or predetermined according to a designimplementation), and may place data that has been encoded and modulatedaccording to the second modulation and coding scheme where normal pilotsymbols would be expected according to the known pilot symbol pattern.

The data stream with data symbols and data modulated pilot symbols maybe transmitted via an antenna 220 on a communication channel, such as aradio communication channel. The communication channel is subject tocertain adverse influences, such as noise that may change the modulatedsignal.

Referring to FIG. 3, an example block diagram 300 of a device 115-a isshown which illustrates various embodiments of the present systems andmethods. The device 115-a may be an example of a communications device115 of FIG. 1. In one embodiment, the system at issue may use QPSK.However, the present systems and methods may be implemented using arange of other modulation schemes.

The device 115-a includes a number of receiver components, which mayinclude: a radio frequency (RF) down-conversion and filtering unit 310,an analog to digital (A/D) unit 315, and a receiver module 320. Theseunits of the device 115-a may, individually or collectively, beimplemented with one or more Application Specific Integrated Circuits(ASICs) adapted to perform some or all of the applicable functions inhardware. Alternatively, the functions may be performed by one or moreother processing units (or cores), on one or more integrated circuits.In other embodiments, other types of integrated circuits may be used(e.g., Structured/Platform ASICs, Field Programmable Gate Arrays(FPGAs), and other Semi-Custom ICs), which may be programmed in anymanner known in the art. The functions of each unit may also beimplemented, in whole or in part, with instructions embodied in amemory, formatted to be executed by one or more general orapplication-specific processors. The device 115-a may include one ormore memory units (not shown) used for a variety of purposes.

In one embodiment, a radio frequency signal may be received via anantenna 305. The desired signal is selected and down-converted andfiltered through the RF down-conversion and filtering unit 310. Theoutput of the filtering unit 310 is the analog baseband (or passband atmuch lower frequency than the original radio frequency) signal, which isconverted into a digital signal by the A/D unit 315. At the receivermodule 320, the digital signal is received and processed to produce astream of data. The receiver module 320 may also perform adaptivedemodulation techniques on signals with data modulated pilot symbolsaccording to embodiments of the present systems and methods.

The data stream may be forwarded to a layer 2/layer 3/additionalprocessing unit 325 for further processing. In one embodiment, thecomponents of the receiver module 320 may be implemented in a single PHYchip. In another embodiment, the RF down-conversion and filtering unit310, A/D unit 315, and components of the receiver module 320 may beimplemented in a single chip with RF and PHY functionality. The receivermodule 320 may include components to adaptively select between differentdemodulation schemes for a plurality of symbols representing thetransmitted codeword. The receiver module 320 may also include adaptiveslicer logic to perform hard decision decoding on the data modulatedsymbols. Further, the receiver module 320 may include components toperform an adaptive log-likelihood ratio (LLR) generation technique togenerate an adaptive number of LLRs for data symbols and data modulatedpilot symbols included in the plurality of received symbols.

FIG. 4 is a block diagram illustrating one embodiment of a receivermodule 320-a, in accordance with the present systems and methods. Thereceiver module 320-a may be an example of the receiver module 320 showin FIG. 3. The receiver module 320-a may include a demodulator 405, aDPLL 410, an LLR generation module 415, and a decoder 420. As previouslyexplained, the receiver module 320-a may receive a signal that has beenconverted to a digital signal by the A/D unit 315.

These components of the receiver module 320-a may, individually orcollectively, be implemented with one or more application-specificintegrated circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on one ormore integrated circuits. In other embodiments, other types ofintegrated circuits may be used (e.g., Structured/Platform ASICs, FieldProgrammable Gate Arrays (FPGAs), and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of each unitmay also be implemented, in whole or in part, with instructions embodiedin a memory, formatted to be executed by one or more general orapplication-specific processors.

At the demodulator 405, the digital signal is received and processed toproduce a stream of data. The demodulator unit 405 may perform symbolsynchronization, Fast Fourier transform (FFT) processing, frequencyoffset correction and estimation, and equalizer functions in any varietyof combinations known in the art. The demodulator 405 may adaptivelyswitch between different demodulation schemes based on the MCS that wasused at the transmitter on a symbol. As a result, the demodulator 405may switch between different demodulation schemes while processing aplurality of symbols representing a single transmitted codeword. Furtherdetails regarding the demodulator 405 will be described below.

The demodulated data (e.g., a plurality of symbols representing thetransmitted codeword) may be input to the DPLL 410. The DPLL 410 maydetermine a phase error of each symbol of the plurality of receivedsymbols. The phase errors may be determined by comparing the angles ofthe received symbols to an estimation of symbols that were transmittedover the air to the device 115. The calculated phase errors may be usedto calculate phase corrections. The phase corrections may correct thephase errors of the symbols of the plurality of received symbols.

In one example, the DPLL 410 may calculate the phase errors of eachsymbol of a current block of received symbols. The phase errors may beused to generate phase corrections. The phase corrections may be appliedto correct the phase errors. In one embodiment, the phase correction foreach symbol may be applied by derotating the corresponding symbol of aplurality of symbols according to the rotation value of the symbol'sphase correction. The phase of the carrier may be recovered by applyingthe symbol's phase correction. Further details regarding the DPLL 410will be described below.

In one embodiment, a plurality of phase-corrected symbols that representa single transmitted codeword may be gathered from the output of theDPLL 410. A plurality of a priori LLRs may be computed from theplurality of phase-corrected symbols by the LLR generation module 415.The a priori LLRs may represent the bits of the transmitted codeword. Inone embodiment, the LLR generation module 415 may generate LLRs for datasymbols and the data modulated pilot symbols included in the pluralityof received symbols.

The plurality of a priori LLRs may be inputted to a decoder 420. Thedecoder 420 may attempt to decode the codeword that was transmitted overthe air to the device 115. The decoded codeword may be provided on afirst output of the decoder 420. In addition, the decoder 420 maygenerate and provide a second output. The second output may include aplurality of a posteriori LLRs (soft LLRs) representing the bits of thetransmitted codeword. The soft LLRs may be used to generate a pluralityof symbols that represent an estimation of the plurality of transmittedsymbols corresponding to the codeword. In one embodiment, symbols may befurther processed by other components of the demodulator 405 and/or DPLL410 before being forwarded to the decoder 420, and in some embodimentsthe transmitted data need not be encoded so there need not be a decoder420.

FIG. 5 is a block diagram illustrating one embodiment of a receivermodule 320-b, in accordance with the present systems and methods. Thereceiver module 320-b may be an example of the receiver module 320 showin FIGS. 3 and/or 4. The receiver module 320-b may include a demodulator405-a, a DPLL 410-a, an LLR generation module 415-a, and a decoder420-a. As previously explained, the receiver module 320-b may receive asignal that has been converted to a digital signal by the A/D unit 315.

These components of the receiver module 320-b may, individually orcollectively, be implemented with one or more application-specificintegrated circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on one ormore integrated circuits. In other embodiments, other types ofintegrated circuits may be used (e.g., Structured/Platform ASICs, FieldProgrammable Gate Arrays (FPGAs), and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of each unitmay also be implemented, in whole or in part, with instructions embodiedin a memory, formatted to be executed by one or more general orapplication-specific processors.

In one configuration, the demodulator 405-a may include a firstdemodulation scheme module 505 and a second demodulation scheme module510. These different demodulation schemes may be adaptively applied to aplurality of received symbols representing a transmitted codeword. Forexample, a first group of data symbols of the plurality of receivedsymbols may have been modulated in a transmitter with a first MCS. Asecond group of data symbols within the plurality of received symbolsmay have been modulated with a second MCS at the transmitter. Thissecond MCS may be a more reliable MCS than the first MCS. The secondgroup of data symbols may occur in place of pilot symbols. Thus, thesymbols within the second group of data symbols may be the datamodulated pilot symbols. In some cases, the second group of data symbolsoccur in place of data symbols. The second group of data symbols mayoccur throughout the plurality of received symbols, such as in place ofpilot symbols and/or data symbols. The demodulator 405-a may demodulatethe plurality of received symbols by switching between differentdemodulation schemes depending on the MCS that was used to modulate thesymbols at the transmitter.

In one example, the output of the demodulator 405-a may be input to theDPLL 410-a. In one configuration, the DPLL 410-a may process theplurality of received symbols to generate phase errors and phasecorrections for the symbols. This may be performed by the angles of thereceived symbols being compared against a reference signal to determinethe phase error of each symbol in the plurality of received symbols. Thereference signal may include hard decision decoding results of thereceived symbols themselves. Because of noisy conditions that may existat the receiver module 320-b, the hard decisions of data symbolscalculated by the DPLL 410-a may be incorrect. As mentioned previously,pilot symbols have been inserted among the data symbols to reduce theoccurrences of erroneous hard decisions. The use of pilot symbols,however, may cause the coding rate of the symbols to increase. The datamodulated pilot symbols (used in place of the pilot symbols) may yieldan improved accuracy of the hard decision while reducing the increase tothe coding rate to maintain the throughput.

The DPLL 410-a may include a pilot symbol identification module 515-a-1and an adaptive slicer module 520. The pilot symbol identificationmodule 515-a-1 may identify when pilot symbols were expected to occurwithin the plurality of received symbols. As described above, inaccordance with the present systems and methods, pilot symbols may bereplaced with data modulated pilot symbols.

The adaptive slicer module 520 may quantize each of the symbols to anearest ideal constellation point, which may be used as an estimation ofthe corresponding transmitted symbols. The output of the adaptive slicermodule 520 may represent the hard decision result for a symbol asdescribed above. In one configuration, the adaptive slicer module 520may be adaptive based on the MCS used for each symbol at thetransmitter. The adaptive capability of the adaptive slicer module 520may allow different hard decision techniques to be used based on the MCSused at the transmitter for the symbols. For example, the adaptiveslicer module 520 may use a first hard decision technique for datasymbols that do not occur when pilot symbols are expected to occur. Whenthe pilot symbol identification module 515-a-1 identifies a time duringwhich a pilot symbol is expected, the adaptive slicer module 520 may usea second technique to perform hard decision on the data modulated pilotsymbols. The hard decisions of the received symbols may be used togenerate the phase errors and phase corrections of these symbols.

In one configuration, the output of the DPLL 410-a may include phasecorrected symbols. These symbols may be collected and inputted to an LLRgeneration module 415-a. The LLR generation module 415-a may alsoinclude a pilot symbol identification module 515-a-2 to identify whenthe pilot symbols are expected to occur among the plurality of phasecorrected symbols. The LLR generation module 415-a may generate a prioriLLRs for each symbol of the plurality of received symbols. Typically,LLRs are not computed for pilot symbols inserted in a data stream. Inaccordance with the present systems and methods, pilot symbols arereplaced with data modulated pilot symbols. As a result, LLRs may becalculated for each symbol of the plurality of received symbols. The LLRgeneration module 415-a may generate a first number of LLRs for datasymbols and a second number of LLRs for the data modulated pilotsymbols. As an example, the LLRs resulting from a data symbol mayinclude 10 bits while the LLRs resulting from a data modulated pilotsymbol may include 6 bits. The pilot symbol identification module515-a-1 may indicate when a data modulated pilot symbol is occurring andthe second number of LLRs may be generated (e.g., 6 bits).

The LLRs generated from the plurality of phase corrected symbols mayrepresent the bits of the transmitted code word. These LLRs may be fedinto the decoder 420-a. The decoder 420-a may use the LLRs to attempt todecode the transmitted codeword.

FIG. 6 is a block diagram illustrating one example of a receiver module320-c that may implement the present systems and methods. In oneembodiment, the receiver module 320-c may be an example of the receivermodule 320 illustrated in FIGS. 3, 4, and/or 5. The receiver module320-c may include a demodulator 405-b, a DPLL 410-b, an LLR generationmodule 415-a, and a decoder 420-b, as previously described. In addition,the receiver module 320-c may include a hard decision module 635 and amodulator 640.

These components of the receiver module 320-c may, individually orcollectively, be implemented with one or more application-specificintegrated circuits (ASICs) adapted to perform some or all of theapplicable functions in hardware. Alternatively, the functions may beperformed by one or more other processing units (or cores), on one ormore integrated circuits. In other embodiments, other types ofintegrated circuits may be used (e.g., Structured/Platform ASICs, FieldProgrammable Gate Arrays (FPGAs), and other Semi-Custom ICs), which maybe programmed in any manner known in the art. The functions of each unitmay also be implemented, in whole or in part, with instructions embodiedin a memory, formatted to be executed by one or more general orapplication-specific processors.

In one configuration, the demodulator 405-b may perform variousprocesses on incoming symbols. For example, the demodulator 405-b mayadaptively switch between different demodulation schemes (e.g., byselecting different modulation scheme modules 505-a, 510-a) based on theMCS used on the incoming symbols at the transmitter. The demodulator405-b may also include an equalizer 605 to perform equalizationtechniques on symbols of a received signal. The output of the equalizer605 (e.g., equalized symbols) may be input to the DPLL 410-b. While FIG.6 illustrates the output of the equalizer 605 being fed into the DPLL410-b, it is to be understood that other implementations may be used.For example, the DPLL 410-b may perform processing on unequalizedsymbols and the equalizer 605 may be placed after the DPLL 410-b in thechain of components of the receiver module 320-c. The DPLL 410-b mayinclude a rotator 610, a phase detector 615, a filter 620, and a voltagecontrolled oscillator (VCO) 625. The DPLL 410-b may be a closed-loopfrequency-control system based on a phase difference between an inputsignal and a feedback signal of the VCO 625.

In one configuration, the DPLL 410-b may perform one or more iterationson a plurality of symbols. Each received plurality of symbols mayrepresent a single codeword transmitted to the device 115. The symbolsmay be constellation points in a QPSK signal that have been rotatedaccording to a random phase caused by the phase noise and frequencyoffset of one or more oscillators in the device 115. In one example, thesymbols may be derotated by the rotator 610. The rotator 610 mayderotate the symbols according to phase correction values generated bythe DPLL 410-b. The phase corrections may be fed back from the VCO 625to the rotator 610. The derotated symbols may be passed to the phasedetector 615.

The phase detector (or phase comparator) 615 may be a frequency mixer,analog multiplier, or logic circuit that generates a voltage signalwhich represents the difference in phase between two signal inputs. Forexample, hard decisions may be performed on the incoming samples. Thesehard decisions may represent estimations of the correspondingtransmitted symbols. The angles of the incoming symbols may be comparedto the estimations of the transmitted symbols based on the harddecisions of the incoming symbols themselves to determine the phaseerrors of the incoming symbols. In one configuration, the phase detector615 may include a pilot symbol identification module 515-b-1 that mayidentify when a pilot symbol is expected to occur among the plurality ofreceived symbols.

When pilot symbols are not expected to occur, an adaptive slicer module520-a may perform hard decision techniques on the data symbols. In oneexample, the adaptive slicer module 520-a may access a first look-uptable (LUT) to determine the nearest ideal constellation point for eachdata symbol. The first look-up table may be associated with a first MCSthat was used on the data symbols at the transmitter. In some cases whenpilot symbols are not expected to occur, the adaptive slicer module520-a may use a first slicer non-LUT function to perform a harddecision. For example, the adaptive slicer module 520-a may use a bittruncation of soft symbols to their nearest constellation symbols or anyother comparator and/or decision logic that yields selecting the closestconstellation symbol for each soft symbol.

When the pilot symbol identification module 515-b-1 indicates that apilot symbol is expected to occur, the adaptive slicer module 520-a mayadaptively switch to access a second look-up table that is associatedwith a second MCS, which is a more reliable MCS than the first MCS. Thesecond look-up table may be accessed to determine the nearest idealconstellation points for the data modulated pilot symbols, which arebeing used in place of the pilot symbols. In some cases when pilotsymbols are expected to occur, the adaptive slicer module 520-a may usea second slicer non-LUT function to perform a hard decision. Forexample, the adaptive slicer module 520-a may use a bit truncation ofsoft symbols to their nearest constellation symbols, or any othercomparator and/or decision logic that yields selecting the closestconstellation symbol for each soft symbol. Because the MCS used on thesedata modulated pilot symbols is more robust, the hard decisions of thesesymbols are less prone to errors than the hard decisions of the datasymbols.

As an example, 1024 Quadrature Amplitude Modulation (QAM) may be the MCSused for the data symbols at the transmitter and 64 QAM may be used forthe data modulated pilot symbols. While 1024 QAM and 64 QAM are used inthis example, it is to be understood that other MCS may be used inaccordance with the various systems and methods described here.

The Euclidian distance between constellation points in 1024 QAM isapproximately four times shorter than the Euclidian distance betweenconstellation points in 64 QAM. As a result, the probability of thephase detector 615 to produce an erroneous hard decision in 1024 QAM,for a given SNR, may be greater than in 64 QAM. In one example, insteadof transmitting a pilot of known sequence, a 64 QAM data symbol may betransmitted. In the phase detector 615 of the receiver module 320-c, ahard decision may be taken on that 64 QAM symbol, which may be lesslikely to be erroneous than the hard decision taken on a 1024 QAM datasymbol. Thus, the accuracy of the phase errors and corrections generatedby DPLL 410-b may increase.

As stated above, the phase detector 615 may detect the difference inphase and frequency between a reference signal (e.g., estimation oftransmitted symbols based on hard decisions of received symbols) and afeedback signal (e.g., a signal input received from the VCO 625). Thephase detector 615 may generate an “up” or “down” control signal basedon whether the feedback frequency is lagging or leading the referencefrequency. These “up” or “down” control signals may determine whetherthe VCO 625 needs to operate at a higher or lower frequency,respectively.

The filter 620 may convert these control signals to a control voltagethat is used to bias the VCO 625. Based on the control voltage, the VCO625 oscillates at a higher or lower frequency, which affects the phaseand frequency of the feedback from the VCO 625. If the phase detector615 produces an up signal, then the frequency of the VCO 625 mayincrease. A down signal decreases the frequency of the VCO 625. The VCO625 may stabilize once the reference signal and the feedback signal havethe same phase and frequency.

In one configuration, in addition to using data modulated pilot symbolsto generate accurate hard decisions to generate an accurate estimationof the transmitted symbols, the output of the decoder 420-b may beutilized to generate the estimation of the transmitted symbols. In oneembodiment, the output of the DPLL 410-b, which includes a plurality ofphase-corrected (derotated) symbols that represent a transmittedcodeword, may be used to generate a plurality of LLRs that represent thebits of the transmitted codeword. This plurality of LLRs may be fed tothe decoder 420-b. LLRs may be generated for both the data symbols andthe data modulated pilot symbols, as described previously. The decoder420-a may implement a forward error correction (FEC) scheme to correcterrors that may be present in the generated LLRs. The decoder 420-b maybe a convolutional turbo code (CTC) decoder, a low-density parity-check(LDPC) decoder, and the like.

In one configuration, the decoder 420-b may produce a first output ofhard decoded bits with a low bit error rate (BER) due to the coding gainof the decoder 420-b. The decoded bits may correspond to the bits thatwere modulated at a transmitting device to generate symbols that weretransmitted over the air to the device 115. In one example, the decodermay include a soft LLR generation module 630. At an additional output ofthe decoder 420-b, the soft LLR generation module 630 may generate anumber of soft a posteriori LLRs which mimic a number of transmittedbits that were modulated in the transmitter device (e.g., the basestation 105). The soft LLRs may be hard decoded and remodulated togenerate a plurality of symbols that represent the plurality of symbolstransmitted over the air to the device 115. As a result, the additionaloutput of the decoder 420-b may include interleaved symbols in a similarsequence that are substantially similar to symbols that were transmittedover the air to the device 115.

In one example, the hard decision module 635 may perform hard decisiondecoding on the soft LLRs. The soft LLRs may be remodulated by themodulator 640 to generate an hypothesis of the transmitted symbols. Thishypothesis may be fed back to the phase detector 615 as referencesymbols. In one configuration, QAM techniques may be performed on thehard decoded soft LLRs to generate the hypothesis of the symbols thatwere transmitted over the air.

Using the feedback of the decoder 420-b, the DPLL 410-c may run a seconditeration on the plurality of received symbols to determine the phaseerrors of these symbols based on the estimation of the correspondingtransmitted symbols. When the plurality of received symbols are fed tothe phase detector 615 during the second iteration, the detector 615 maydetermine the phase errors of the symbols by comparing the angles of thesymbols with the angles of the reference symbols received from thefeedback loop of the decoder 420-b. The reference symbols may representan estimation of the symbols that were transmitted over the air to thedevice 115. Based on the generated phase errors of the received symbols,phase corrections may be generated for the symbols of the plurality ofreceived symbols. In one embodiment, the DPLL 410-b may run a singleiteration on a plurality of received symbols when data modulated pilotsymbols are used in lieu of pilot symbols.

FIG. 7 is a block diagram of a system 700 including a base station 105-band a mobile device 115-b. This system 700 may be an example of thesystem 100 of FIG. 1. The base station 105-b may be equipped withantennas 734-a through 734-x, and the mobile device 115-b may beequipped with antennas 752-a through 752-n. At the base station 105-b, atransmit processor 720 may receive data from a data source.

The transmit processor 720 may process the data. The transmit processor720 may also generate reference symbols, and a cell-specific referencesignal. A transmit (TX) MIMO processor 730 may perform spatialprocessing (e.g., precoding) on data symbols, control symbols, and/orreference symbols, if applicable, and may provide output symbol streamsto the transmit modulator/demodulators 732-a through 732-x. Each basestation modulator/demodulator 732 may process a respective output symbolstream to obtain an output sample stream. Each base stationmodulator/demodulator 732 may further process (e.g., convert to analog,amplify, filter, and upconvert) the output sample stream to obtain adownlink (DL) signal. In one example, DL signals from base stationmodulator/demodulators 732-a through 732-x may be transmitted via theantennas 734-a through 734-x, respectively.

At the mobile device 115-b, the mobile device antennas 752-a through752-n may receive the DL signals from the base station 105-b and mayprovide the received signals to the mobile device modulator/demodulators754-a through 754-n, respectively. Each mobile devicemodulator/demodulator 754 may condition (e.g., filter, amplify,downconvert, and digitize) a respective received signal to obtain inputsamples. Each mobile device modulator/demodulator 754 may furtherprocess the input samples to obtain received symbols. A MIMO detector756 may obtain received symbols from all the mobile devicemodulator/demodulators 754-a through 754-n, perform MIMO detection onthe received symbols if applicable, and provide detected symbols. Areceive processor 758 may process (e.g., demodulate, deinterleave, anddecode) the detected symbols, providing decoded data for the mobiledevice 115-b to a data output, and provide decoded control informationto a processor 780, or memory 782.

On the uplink (UL), at the mobile device 115-b, a transmit processor 764may receive and process data from a data source. The transmit processor764 may also generate reference symbols for a reference signal. Thesymbols from the transmit processor 764 may be precoded by a transmitMIMO processor 766 if applicable, further processed by the mobile devicemodulator/demodulators 754-a through 754-n (e.g., for SC-FDMA, etc.),and be transmitted to the base station 105-b in accordance with thetransmission parameters received from the base station 105-b. At thebase station 105-b, the UL signals from the mobile device 115-b may bereceived by the antennas 734, processed by the transmitmodulator/demodulators 732, detected by a MIMO detector 736 ifapplicable, and further processed by a receive processor. The receiveprocessor 738 may provide decoded data to a data output and to theprocessor 740. In one configuration, the receive processor 758 mayinclude a demodulator 405-c, a DPLL 410-c, and an LLR generation module415-c to implement the systems and methods described herein. Thedemodulator 405-c, DPLL 410-c, and LLR generation module 415-c may beexamples of the demodulator 405-c, DPLL 410-c, and an LLR generationmodule 415-c described in FIGS. 4, 5, and/or 6. The components of themobile device 115-b may, individually or collectively, be implementedwith one or more Application Specific Integrated Circuits (ASICs)adapted to perform some or all of the applicable functions in hardware.Each of the noted modules may be a means for performing one or morefunctions related to operation of the system 700. Similarly, thecomponents of the base station 105-b may, individually or collectively,be implemented with one or more Application Specific Integrated Circuits(ASICs) adapted to perform some or all of the applicable functions inhardware. Each of the noted components may be a means for performing oneor more functions related to operation of the system 700.

FIG. 8 is a flow chart illustrating one example of a method 800 tomitigate an unwanted increase in a coding rate of a wirelesscommunication signal in accordance with the present systems and methods.For clarity, the method 800 is described below with reference to themobile device 115 of FIGS. 1, 3, and/or 7. In one implementation, thereceiver module 320 of FIGS. 3, 4, 5 and/or 6 may execute one or moresets of codes to control the functional elements of the mobile device115 to perform the functions described below.

In one configuration, at block 805, a plurality of symbols including atransmitted codeword may be received. The plurality of symbols mayinclude a first group of data symbols with a first MCS and a secondgroup of data modulated pilot symbols with a second MCS. A carrier phaseerror may be determined based at least in part on the second group ofdata modulated pilot symbols. The second MCS may be a more reliable,robust MCS than the first MCS. The second group of data symbols may beused instead of pilot symbols. At block 810, switching betweenapplicable demodulation schemes may adaptively occur for each group ofthe plurality of symbols.

Therefore, the method 800 may provide for the minimization of a codingrate because data symbols of a data stream are not replaced with pilotsymbols, which do not carry data. Instead, data modulated pilot symbolsare used to carry data. Thus, the coding rate may be lower than if pilotsymbols replaced data symbols. It should be noted that the method 800 isjust one implementation and that the operations of the method 800 may berearranged or otherwise modified such that other implementations arepossible.

FIG. 9 is a flow chart illustrating one example of a method 900 toimprove accuracy of hard decisions of symbols of a wirelesscommunication signal in accordance with the present systems and methods.For clarity, the method 900 is described below with reference to themobile device 115 of FIGS. 1, 3, and/or 7. In one implementation, thereceiver module 320 of FIGS. 3, 4, 5 and/or 6 may execute one or moresets of codes to control the functional elements of the mobile device115 to perform the functions described below.

In one configuration, at block 905, a plurality of symbols including atransmitted codeword may be received. The plurality of symbols mayinclude a first group of data symbols with a first MCS and a secondgroup of data modulated pilot symbols with a second MCS. A carrier phaseerror may be determined based at least in part on the second group ofdata modulated pilot symbols. The second MCS may be a more reliable,robust MCS than the first MCS. The second group of data symbols may beused instead of pilot symbols. At block 910, a determination may be madefor each symbol as to whether the symbol occurs when a pilot symbol isexpected to occur. If, at decision 915, a symbol does not occur when apilot symbol is expected, a first look-up table for the first MCS may beaccessed at block 920. At block 925, hard decision decoding may beperformed on the symbol using the first look-up table. In some cases, atblock 920 and 925 a first non-LUT function may be used for hard decisiondecoding on the symbol. If, however, it is determined that the symboloccurs when a pilot symbol is expected to occur, a second look-up tablefor the second MCS is accessed at block 930. Hard decision decoding ofthe symbol is performed at block 935 using the second look-up table. Insome cases, at block 930 and 935 a second non-LUT function may be usedfor hard decision decoding on the symbol.

At block 940, phase errors are generated for the plurality of receivedsymbols using the results of the hard decision decoding. At block 945,phase corrections are generated for the plurality of received symbolsbased on the generated phase errors.

Therefore, the method 900 may provide for accurate hard decisions ofsymbols by using data modulated pilot. It should be noted that themethod 900 is just one implementation and that the operations of themethod 900 may be rearranged or otherwise modified such that otherimplementations are possible.

FIG. 10 is a flow chart illustrating one example of a method 1000 toimprove the decoding of a codeword in accordance with the presentsystems and methods. For clarity, the method 1000 is described belowwith reference to the mobile device 115 of FIGS. 1, 3, and/or 7. In oneimplementation, the receiver module 320 of FIGS. 3, 4, 5 and/or 6 mayexecute one or more sets of codes to control the functional elements ofthe mobile device 115 to perform the functions described below.

In one configuration, at block 1005, a plurality of phase correctedsymbols are gathered together. The phase corrected symbols may include atransmitted codeword. The phase corrected symbols may be gathered at theoutput of the DPLL 410.

At block 1010, a determination may be made for each phase correctedsymbol whether the symbol occurs when a pilot symbol is expected tooccur. If, at decision, 1015, it is determined that the symbol does notoccur when a pilot is expected, at block 1020, a first number of apriori LLRs may be generated from the symbol. If, however, it isdetermined that the symbol does occur when a pilot symbol is expected,at block 1025, a second number of a priori LLRs may be generated fromthat symbol.

At block 1030, the plurality of LLRs may be fed to a decoder to decodethe transmitted codeword. At block 1035, a plurality of soft aposteriori LLRs may be generated at the output of the decoder. The softLLRs may represent a plurality of bits of the transmitted codeword. Atblock 1040, an estimation of a plurality of transmitted symbols may begenerated based on the output of the decoder (e.g., the soft LLRs).

Therefore, the method 1000 may improve the decoding of a transmittedcodeword by generating a priori LLRs for each symbol in the plurality ofreceived symbols. It should be noted that the method 1000 is just oneimplementation and that the operations of the method 1000 may berearranged or otherwise modified such that other implementations arepossible.

Techniques described herein may be used for various wirelesscommunications systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, andother systems. The terms “system” and “network” are often usedinterchangeably. A CDMA system may implement a radio technology such asCDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases 0 and Aare commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) iscommonly referred to as CDMA2000 1×EV-DO, High Rate Packet Data (HRPD),etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. ATDMA system may implement a radio technology such as Global System forMobile Communications (GSM). An OFDMA system may implement a radiotechnology such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA),IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM□, etc.UTRA and E-UTRA are part of Universal Mobile Telecommunication System(UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are newreleases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, andGSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). CDMA2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). The techniques described herein may be used for thesystems and radio technologies mentioned above as well as other systemsand radio technologies. The description below, however, describes an LTEsystem for purposes of example, and LTE terminology is used in much ofthe description below, although the techniques are applicable beyond LTEapplications.

Examples of Radio Access Technologies employing CDMA techniques includeCDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases 0 and Aare commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) iscommonly referred to as CDMA2000 1×EV-DO, High Rate Packet Data (HRPD),etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA.Examples of TDMA systems include various implementations of GlobalSystem for Mobile Communications (GSM). Examples of Radio AccessTechnologies employing FDMA and/or OFDMA include Ultra Mobile Broadband(UMB), Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of UniversalMobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE)and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA,E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from anorganization named “3rd Generation Partnership Project” (3GPP). CDMA2000and UMB are described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). The techniques describedherein may be used for the systems and radio technologies mentionedabove as well as other systems and radio technologies.

The description provided above provides examples, and is not limiting ofthe scope, applicability, or configuration set forth in the claims.Changes may be made in the function and arrangement of elementsdiscussed without departing from the spirit and scope of the disclosure.Various embodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, the methods described may beperformed in an order different from that described, and various stepsmay be added, omitted, or combined. Also, features described withrespect to certain embodiments may be combined in other embodiments.

The detailed description set forth above in connection with the appendeddrawings describes exemplary embodiments and does not represent the onlyembodiments that may be implemented or that are within the scope of theclaims. The term “exemplary” used throughout this description means“serving as an example, instance, or illustration,” and not “preferred”or “advantageous over other embodiments.” The detailed descriptionincludes specific details for the purpose of providing an understandingof the described techniques. These techniques, however, may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the described embodiments.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope and spirit of the disclosure and appended claims. For example,due to the nature of software, functions described above can beimplemented using software executed by a processor, hardware, firmware,hardwiring, or combinations of any of these. Features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C).

Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation,computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable aperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Throughout this disclosure the term “example” or“exemplary” indicates an example or instance and does not imply orrequire any preference for the noted example. Thus, the disclosure isnot to be limited to the examples and designs described herein but is tobe accorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication, comprising:receiving a plurality of symbols comprising a transmitted codeword, theplurality of symbols including a first group of symbols comprising datasymbols with a first modulation and coding scheme and a second group ofsymbols comprising data modulated pilot symbols with a second modulationand coding scheme, wherein the second group of data modulated pilotsymbols are used in lieu of pilot symbols; adaptively switching betweenapplicable demodulation schemes for the first group of symbols and thesecond group of symbols; performing hard decision decoding for theplurality of symbols; generating phase errors for the plurality ofsymbols using results of the hard decision decoding; and generatingphase corrections for the plurality of symbols based at least in part onthe generated phase errors.
 2. The method of claim 1, furthercomprising: determining a carrier phase error based at least in part onthe data modulated pilot symbols.
 3. The method of claim 1, wherein thesecond modulation and coding scheme is a more reliable modulation andcoding scheme than the first modulation and coding scheme.
 4. The methodof claim 1, wherein adaptively switching between the demodulationschemes comprises: determining, for a symbol of the plurality ofsymbols, whether the symbol occurs when a pilot symbol is expected tooccur.
 5. The method of claim 4, wherein performing hard decisiondecoding for the plurality of symbols comprises: upon determining thatthe symbol does not occur when a pilot symbol is expected to occur,using a first look-up table (LUT) or a first non-LUT function for thefirst modulation and coding scheme to perform hard decision decoding ofthe symbol; and upon determining that the symbol does occur when a pilotsymbol is expected to occur, using a second look-up table or a secondnon-LUT function for the second modulation and coding scheme to performhard decision decoding of the symbol.
 6. The method of claim 1, furthercomprising: derotating the symbols of the plurality of received symbolsto generate a plurality of phase corrected received symbols according tothe generated phase corrections.
 7. The method of claim 6, furthercomprising: generating a plurality of a priori log-likelihood ratios(LLRs) from the plurality of phase corrected received symbols, theplurality of a priori LLRs representing a plurality of bits of thetransmitted codeword.
 8. The method of claim 7, wherein generating theplurality of a priori LLRs comprises: determining, for a phase correctedsymbol of the plurality of phase corrected symbols, whether the phasecorrected symbol occurs when a pilot symbol is expected to occur.
 9. Themethod of claim 8, further comprising: upon determining that the phasecorrected symbol does not occur when a pilot symbol is expected tooccur, generating a first number of a priori LLRs from the phasecorrected symbol; and upon determining that the phase corrected symboldoes occur when a pilot symbol is expected to occur, generating a secondnumber of a priori LLRs from the phase corrected symbol, the secondnumber of a priori LLRs being less than the first number of a prioriLLRs.
 10. The method of claim 7, further comprising: feeding theplurality of a priori LLRs to a decoder to decode the transmittedcodeword; and collecting a plurality of soft a posteriori LLRs at anoutput of the decoder, the soft a posteriori LLRs representing theplurality of bits of the transmitted codeword.
 11. A receiving devicefor wireless communication, comprising: a processor; memory inelectronic communication with the processor; and instructions stored inthe memory, the instructions being executable by the processor to:receive a plurality of symbols comprising a transmitted codeword, theplurality of symbols including a first group of symbols comprising datasymbols with a first modulation and coding scheme and a second group ofsymbols comprising data modulated pilot symbols with a second modulationand coding scheme, wherein the second group of data modulated pilotsymbols are used in lieu of pilot symbols; adaptively switch betweenapplicable demodulation schemes for the first group of symbols and thesecond group of symbols; perform hard decision decoding for theplurality of symbols; generate phase errors for the plurality of symbolsusing results of the hard decision decoding; and generate phasecorrections for the plurality of symbols based at least in part on thegenerated phase errors.
 12. The device of claim 11, wherein theinstructions are executable by the processor to: determine a carrierphase error based at least in part on the data modulated pilot symbols.13. The device of claim 11, wherein the second modulation and codingscheme is a more reliable modulation and coding scheme than the firstmodulation and coding scheme.
 14. The device of claim 11, wherein theinstructions to adaptively switch between the demodulation schemes areexecutable by the processor to: determine, for a symbol of the pluralityof symbols, whether the symbol occurs when a pilot symbol is expected tooccur.
 15. The device of claim 14, wherein the instructions to performhard decision decoding for the plurality of symbols are executable bythe processor to: upon determining that the symbol does not occur when apilot symbol is expected to occur, use a first look-up table or a firstnon-LUT function for the first modulation and coding scheme to performhard decision decoding of the symbol; and upon determining that thesymbol does occur when a pilot symbol is expected to occur, use a secondlook-up table or a second non-LUT function for the second modulation andcoding scheme to perform hard decision decoding of the symbol.
 16. Thedevice of claim 11, wherein the instructions are executable by theprocessor to: derotate the symbols of the plurality of received symbolsto generate a plurality of phase corrected received symbols according togenerated phase corrections for the symbols.
 17. The device of claim 16,wherein the instructions are executable by the processor to: generate aplurality of a priori log-likelihood ratios (LLRs) from the plurality ofphase corrected received symbols, the plurality of a priori LLRsrepresenting a plurality of bits of the transmitted codeword.
 18. Thedevice of claim 17, wherein the instructions to generate the pluralityof a priori LLRs are executable by the processor to: determine, for aphase corrected symbol of the plurality of phase corrected symbols,whether the phase corrected symbol occurs when a pilot symbol isexpected to occur.
 19. The device of claim 18, wherein the instructionsto generate the phase errors are executable by the processor to: upondetermining that the phase corrected symbol does not occur when a pilotsymbol is expected to occur, generate a first number of a priori LLRsfrom the phase corrected symbol; and upon determining that the phasecorrected symbol does occur when a pilot symbol is expected to occur,generate a second number of a priori LLRs from the phase correctedsymbol, the second number of a priori LLRs being less than the firstnumber of a priori LLRs.
 20. The device of claim 17, wherein theinstructions are executable by the processor to: feed the plurality of apriori LLRs to a decoder to decode the transmitted codeword; and collecta plurality of soft a posteriori LLRs at an output of the decoder, thesoft a posteriori LLRs representing the plurality of bits of thetransmitted codeword.